Although potassium channel openers such as minoxidil promote hair growth in vivo, the mechanisms by which they do so are unclear. Using a red deer whole hair follicle culture system we have previously demonstrated that the potassium channel openers, minoxidil and diazoxide stimulate hair follicle growth in vitro.

In order to further explore the role of potassium channels in hair growth, we have investigated the effect of the potassium channel blocker, tolbutamide on red deer hair growth in organ culture. Anagen follicles were microdissected from the mane of 6 red deer stags, washed with sterile phosphate buffered saline, and incubated in Williams E medium supplemented with 5 mM glucose, 100 U/ml penicillin and 2.5 ug/ml amphoterin B. A minimum of six follicles were incubated in each experimental group; control vehicle (0.01 % dimethylsulphoxide), 0.1, 1, 10, 100 uM minoxidil, tolbutamide (1 mM), or minoxidil (10 uM) + tolbutamide (1 mM). Hair follicles grew under all experimental conditions for up to 8 days.

Follicles consistently grew faster in the presence of all concentrations of minoxidil compared to control conditions. In contrast, tolbutamide slowed follicle growth compared to the vehicle control.

Incubation of isolated follicles with a combination of minoxidil and tolbutamide resulted in an inhibition of the stimulatory effects of minoxidil; the follicles grew at the same rate as the control follicles.

The stimulatory effect of minoxidil at 4 different concentrations supports our earlier studies using this culture system. The absence of any growth potentiation by minoxidil in the presence of the potassium blocker, tolbutamide, implies that minoxidil is stimulating hair growth in this system via potassium channels. Further studies should help us to elucidate the exact mechanisms involved in the stimulation hair growth by minoxidl.